French patent application 2 290 366 discloses a device enabling two substances to be stored separately, to be mixed together, and the resulting mixture to be dispensed, that device comprising a necked receptacle containing one of the substances and a perforated plate made of a semi-rigid plastics material such as polyvinyl chloride, containing the other substance and disposed on the neck of the receptacle.
A pushbutton is provided to tear off a tab closing the perforated plate and to enable the substance contained therein to fall into the receptacle and be mixed with the other substance.
Also known, from French patent application FR 2 722 765 in the name of the Applicant company, is a device comprising a receptacle and a removable shutter placed inside the receptacle for separating two chambers respectively containing the two substances prior to first use. On first use of the device the shutter is removed or torn by means of a pushbutton so as to put said chambers into communication and enable said substances to be mixed together. On each occasion that the pushbutton is depressed, it is also advantageously used to establish a pressure rise within the receptacle and the expulsion of a predetermined quantity of the mixture. A return spring enables the pushbutton to be returned to its initial position when the user releases it. Typically, since at least one of the two substances is a liquid, it is necessary for the pushbutton to move in sealed manner relative to the receptacle so as to avoid any leakage. Sealing is obtained by the pushbutton being an exact fit in a cylindrical portion of the receptacle, and, if necessary, sealing is reinforced by the presence of a sealing skirt surrounding said cylindrical portion. A tamperproofing ring can prevent the pushbutton being moved so long as the ring is present on the receptacle. Such a device has rather a large number of component parts and it is therefore relatively expensive to manufacture and to assemble.